In some situations, it is desirable to be able to mount an accessory on a firearm. The most common type of accessory is a sight or scope that can increase the accuracy with which a person can aim the firearm. The person views an intended target through the sight or scope in association with a reticle, often with a degree of magnification.
Accessories such as firearm sights are usually aftermarket devices that need to be mounted on the firearm after the manufacturer has made and shipped the firearm. Usually, it is the end user who selects and mounts the accessory on the firearm. In some circumstances, a person may want to be able to quickly switch from one accessory to another, for example from one sight to another sight. Therefore, it has become relatively standard for firearm manufacturers to provide an accessory mounting rail on the firearm. The rail is usually provided on the “receiver” of the firearm, or in other words the part of the firearm that carries the bolt.
One very common type of mounting rail is known in the industry as a Picatinny rail. Although the Picatinny rail is effectively an industry standard, the industry specification for the Picatinny rail is not particularly precise. For example, it includes a drawing that has some dimensional errors. As a result, Picatinny rails vary somewhat in dimension from manufacturer to manufacturer, and even among different versions of a Picatinny rail made by the same manufacturer.
Many firearm accessories such as sights and scopes are provided with mounting arrangements that are designed to cooperate with a Picatinny rail. While these existing mounting arrangements have been generally adequate for their intended purposes, they have not been satisfactory in all respects.
For example, some have one or more knobs that each need to be rotated through several 360° revolutions in order to couple or decouple the mounting arrangement to the rail. Devices of this type cannot be mounted to and dismounted from a rail as rapidly as is sometimes desirable.
A further consideration is that, due to the dimensional variations among different Picatinny rails, some mounting arrangements will tightly and securely grip some Picatinny rails, but cannot tightly and securely grip other Picatinny rails. In some cases, if a particular Picatinny rail happens to be on the large side, a user may have to press hard on a lever or other actuating member in order to get the clamping mechanism to properly lock onto the rail. The force exerted on the lever can sometimes cause the lever to break.
Still other mounting arrangements have a cam or other clamping part that, as it moves into a clamping position, rubs along the side of the Picatinny rail, thereby abrading the side of the rail. This can mar and/or burnish the rail, which in turn can reduce the ability of the rail to be tightly and securely gripped by the mounting arrangement.